The invention relates to a process for decontaminating transition metals contaminated with parts per million concentrations of radioactive elements and, more particularly, to an electrochemical process for decontaminating metals contaminated with radioactive elements such as technetium which tend to plate along with the metal to be decontaminated.
Of particular interest to the present invention is the remediation of radio-contaminated nickel from decommissioning uranium gas diffusion cascades in which nickel is the primary constituent. This is a unique application of metals decontamination from an uncommon source; viz, DOE-DP diffusion cascades. Several such cascades exist; none have, heretofore, been decontaminated. However, the decontamination art taught herein applies equally well to the recovery and decontamination of other multivalent, strategic metals which can be electrowon such as tin, copper, cobalt, chromium, iron, zinc, lead and like transition metals.
The sources of radio-contamination in diffusion barrier nickel generally include uranium with enrichment levels above natural levels (usually about 0.7%) and reactor fission daughter products, such as Tc, Np, Pu, and any other actinides. Because Tc is a man-made (not natural) element, it presents unique challenges for nickel decontamination. For example, contaminated nickel may have an activity due to about 1-5 ppm technetium of up to about 5000 Bq/gm or more, which is more than two orders of magnitude above the maximum international release criteria of 74 Bq/gm metal total activity. Certain countries have specified an even lower criteria of 1.0 Bq/gm or less total activity. If the total activity of a metal exceeds the release criteria, then it is subject to government control for the protection of the public and is considerably less valuable. Because electrochemical plating is required to win back Ni metal, and because Tc has similar electrochemical properties to Ni, new technical apparatus to metal processing are required for these applications.